In view of the nature of spike activity of oxytocinergic neurosecretory neurons and episodic oxytocin secretion in the face of constant mammary receptor stimulation during suckling, the question arises why oxytocin is not secreted under those conditions at a constant elevated output. Previous work suggests the possibility of the existence of central gating systems or gating in the afferent milk ejection pathway, which regulate oxytocinergic neuron activation and oxytocin secretion. This possibility is amenable to investigation by classical neurophysiological and endocrine methods. In the proposed study, neural gating mechanisms will be studied at several levels within the central nervous system and at the level of peripheral receptors in order to aid in the resolution of the question whether and to what extent afferent fibers determine the manner of activation of oxytocinergic neurosecretory neurons and to account for their episodic activation and oxytocin secretory pattern. This will include (a) examination of the discharge pattern of oxytocin secreting neurons in relation to stimuli applied to central nervous sites and their interaction with simultaneous peripheral mammary receptor input, (b) examination of the central neuronal discharge pattern during transmission of mammary receptor input via spinal afferent fibers, and (c) examination of the discharge pattern from mammary receptors and the effect of simultaneous stimulation by different sensory modalities. This approach is expected to aid the understanding of the milk ejection reflex by providing clearer definitions of sites and mechanisms of interaction of central nervous regulatory systems. As well it is hoped that this study can form the basis for further investigation of other neuroendocrine regulatory systems.